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W.J. van der Burg

1

, J. de Freitas

2

, A.O. Debrot

3

, L.A.P. Lotz

1

Plant Research International, part of Wageningen UR PRI report 437

Business Unit Agrosystems Research Imares report C185/11

January 2012

Naturalised and invasive alien plant species in the Caribbean Netherlands: status, distribution,

threats, priorities and recommendations

Report of a joint Imares/Carmabi/PRI project financed by the Dutch Ministry of Economic Affairs, Agriculture & Innovation

1 Plant Research International, Wageningen, the Netherlands

2 Carmabi, Caribbean Research & Management of Biodiversity, Curaçao

3 Imares, Institute for Marine Research, IJmuiden, the Netherlands

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© 2012 Wageningen, Foundation DLO research institute Plant Research International. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of DLO, Plant Research International, Business Unit Agrosystems Research.

The Foundation DLO is not responsible for any damage caused by using the content of this report.

Research funded by the Netherlands Ministry of Economic Affairs, Agriculture and Innovation Project code BO-11-11-05-004

Frontispiece: Lot for sale in Saba

Photography by W.J. van der Burg unless stated otherwise

Plant Research International, part of Wageningen UR Business Unit Agrosystems Research

Address : P.O. Box 616, 6700 AP Wageningen, the Netherlands

: Wageningen Campus, Droevendaalsesteeg 1, Wageningen, the Netherlands Tel. : +31 317 48 05 56 / 48 08 42

Fax : +31 317 48 10 47 E-mail : info.pri@wur.nl Internet : www.pri.wur.nl

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Table of contents

page

Executive summary 1

1. Introduction, why this study 4

1.1. The Caribbean Netherlands and biodiversity 4

1.2. Aim of this study 4

2. Research approach 5

2.1 Definitions of exotic species, alien species, invasive species, invasive exotic species. 5

2.1.1. The invasion process 5

2.1.2. Phases of invasion: the basis for a classification of invasive species. 6

2.2. Field visits and information sources 8

2.3. Stakeholders consultation 8

2.4. Literature search 8

2.5. How we report the results 8

3. The islands: general 10

3.1. Bonaire 10

3.2. Saba 11

3.3. St. Eustatius 13

3.4. Other Dutch Caribbean 15

3.4.1. St. Marten 15

3.4.2. Aruba 16

3.4.3. Curacao 17

4. Naturalised and invasive exotic plants 18

4.1. Results 18

4.1.1. Alphabetical list of invasive plant species 18

4.1.2. Most important problem species 48

4.1.3. Potential invasives, weeds and flora contamination 58

4.2. Recommendations/priorities 62

4.2.1. General recommendations 62

4.2.2. Aruba 64

4.2.3. Bonaire 64

4.2.4. Curacao 65

4.2.5. St. Eustatius 65

4.2.6. Saba 65

4.2.7. St. Marten 66

5. General conclusions 67

6. Acknowledgements 68

7. Literature 69

Appendixes 78

I. List of consulted stakeholders 78

II. Alien plants with invasive behaviour relevant for the Caribbean Netherlands 80

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Executive summary

The Netherlands are signatories of the international Convention on Biological Diversity (CBD).

This implies that the nation will protect biodiversity on its territory. This includes the protection of natural fauna and vegetation from negative impact caused by invasive alien species (see 2.1.

for a definition). By 10-10-2010 the BES islands (Bonaire, St Eustatius and Saba) became

‘special municipalities’ of the Netherlands. They together form “Caribisch Nederland” (Caribbean Netherlands, Hulanda Karibe). Due to this stronger link to the Netherlands many responsibilities have moved from the Antillean government to the Netherlands. This includes important responsibilities with respect to the protection of nature.

The present study was financed by the Dutch Ministry of Economic Affairs, Agriculture and Innovation and included a literature study, a field trip and writing of the present document with main observations, conclusions and recommendations. A major part of the report consists of an alphabetical list of (known) invasives with their current status (4.1.1.).

Apart from the three islands belonging to Caribisch Nederland, for completeness, some attention is given to Aruba, Curacao and St. Maarten as well (esp. in 4.1.1. and Appendix II).

Stages of invasion

In order to define the problem of invasive alien (non-native) species of plants more accurately it is relevant to recognise the following categories:

Exotic

Species that are not part of the natural indigenous vegetation are called exotics. Examples are introductions as ornamental or agricultural species. If contained within the confines of gardens and farms, these species are not considered problematic.

Established

Species that occur ‘in the wild’, i.e. outside the control of cultivation or husbandry and are able to reproduce themselves resulting in new individuals, we call established (present). Species can stay in this phase, the ‘lag phase’ (see 2.1), for quite some time. It is the stage in which the species adapts to its new environment using its genetic flexibility.

At this stage complete eradication is still an option, because the number of individuals and locations is limited. This means that the costs can be relatively low, compared to eradication at a later stage.

Naturalised

If given enough time, species may start to adapt genetically to the new environment, by optimising its physiology and/or growth habit. As a result the species will start spreading more rapidly and effectively and becoming part of the natural flora. In most cases this is not considered a major problem; the plants will get their own function within the ecology of the island and will not replace indigenous species entirely. Moreover, the costs of complete eradication have become prohibitive at this stage, so only containment is an option.

Invasive

It is generally believed that about one in one thousand exotics becomes really problematic, e.g.

with respect to environmental, ecological or economical impact (Williamson 1995). They start to grow out of control, massively invade natural habitats and reduce or eliminate native species.

They have broken down the dispersal barrier and have become invasive.

At this stage one can only try to achieve a stage of equilibrium, of mitigation, by intensive control measures. These are usually limited by financial resources, and can normally only be

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successful with commitment of the local society, e.g. shown by the enthusiastic support and hand labour of many volunteers.

Invasives of the Caribbean Netherlands

In this report 65 species of invasives are enumerated (4.1.1.) with their history and properties, based on a literature survey and completed with experience and findings of the authors. Four of the main problematic species are treated more extensively in 4.1.2. These are the Coral vine (Antigonon leptopus) which poses a great threat to nature, especially in St. Eustatius; the Rubber vine (Cryptostegia grandiflora) which is able to overgrow and smother shrubs and trees and is especially spreading on the Leeward Islands; the neem tree (Azadirachta indica) which is planted for shade and medicinal purposes, but is escaping on Bonaire; and ‘Donna grass’

(Bothriochloa pertusa) which is a very problematic species replacing the more palatable local grasses on the Windward Islands, most notably on St. Eustatius.

In a complementary list a further 80 species that need more investigation are mentioned (4.1.3.). This list is not complete but it enumerates species that are present on at least one of the islands. They need special attention because it is best to prevent them from entering at all or to eliminate the few plants or populations that have established themselves. Some species in this list are already present at some scale, like some of the arable weeds, but need careful monitoring to prevent them from entering nature.

A general problem are the free-roaming animals, cows, donkeys and especially goats (all non- native species) that are destroying nature in an uncontrolled way. Their presence has a detrimental effect on biodiversity, eating young seedlings and trees, and thereby preventing the natural regeneration and succession. Moreover, the bare soils that result are susceptible to water and wind erosion; material that is deposited in the surrounding seas.

Management options

Before an exotic has been introduced prevention is the most important action, i.e. keep the chance that exotic species may be introduced as low as possible. As soon as a first introduction has been realised and the exotic still occurs at low densities at few sites, eradication after first observation will be the most important action. Finally, if an exotic has already spread over different sites or even different habitats and has increased in densities, eradication might not be an achievable option anymore. Then containment and population management will be the most relevant actions to minimise the negative impact (mitigation). In general, prevention will generate the most cost-effective options to avoid problems due to invasive exotic plants (Davis 2009).

The main observations are:

Prevention

Prevention plans need to be developed with regulations restricting the import of exotic species.

This includes the development of ‘Black lists’ for the Leeward and Windward Islands respectively.

Public awareness (customs and other officials, general public, landscapers, new inhabitants) must be raised and alternatives for imported exotics must be offered.

Agricultural departments and customs offices on all islands are understaffed and not able to control the many routes through which exotics enter.

Eradication after first observation

Rapid first observation of an exotic plant after introduction into the wild is essential for the success of an eradication action. Therefore a ‘Watch list’ or ‘Grey List’ needs to be developed.

Since the difference in climates, these watch lists will partly differ between islands and differ even more between the Leeward and Windward islands.

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Also knowledge about the natural flora and invasives must be increased through education, at schools as well as for professionals (rangers, customs personnel, agricultural department, etc.).

Floras for the Windward Islands are outdated and not accessible.

Containment/population management

Management plans need to be developed for the control Antigonon, Cryptostegia and neem to be able to stop further spreading and to mitigate the impact on nature.

Research on the life cycle of invasives and experiments for their control have to be carried out.

The problem of roaming animals must be tackled. Small island communities are not able to do this without outside assistance.

If chemical control is considered, special Dutch Caribbean regulations apply based on restricted import permissions for crop protection agents.

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1. Introduction, why this study

1.1. The Caribbean Netherlands and biodiversity

The Netherlands are signatories of the international Convention on Biological Diversity (CBD).

This implies that the nation will protect biodiversity on its territory. This includes the protection of natural fauna and vegetation from negative impact caused by invasive alien species (see 2.1.

for a definition). By 10-10-2010 the BES islands (Bonaire, St Eustatius and Saba) became

‘special municipalities’ of the Netherlands. They together form “Caribisch Nederland” (Caribbean Netherlands, Hulanda Karibe). Due to this stronger link to the Netherlands many responsibilities have moved from the Antillean government to the Netherlands. This includes important responsibilities with respect to the protection of nature.

1.2. Aim of this study

This study aims at establishing the status of invasive plant species and their effect on the vegetative terrestrial ecosystem, as well as an analysis of the major bottlenecks and possibilities for management or mitigation.

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2. Research approach

2.1 Definitions of exotic species, alien species, invasive species, invasive exotic species.

Much literature is available on exotic species and many different terms are used to refer to the same, or almost the same. After a short description of the invasion process we will discuss the definitions briefly which are the basis for the classification in this report.

2.1.1. The invasion process

A number of invasive plant species are present in the Caribbean Netherlands. Some are aggressively invading areas, others are perhaps in the ‘lag phase’ of establishment, and still others will never pose a problem. The behaviour, now or in the future, depends largely on two factors: the invasivity of a species and the invasibility of the environment. It is the interaction between these two that determines whether a plant becomes invasive (Davis 2009).

The invasivity, or the invasive strength, of a plant depends on its various characters. In time, these may vary or change in a population, rendering the plant more invasive after some time.

This phenomenon is called the ‘lag phase’ of invasiveness (Figure 1). This may be caused by a genetic shift to adapt to the local conditions. Low genetic diversity at the start may cause a delay in the adaptation process, while plants coming in at larger numbers being able to adapt more quickly because of a greater chance of having the right genes in the population. But there can be other reasons why a plant may not be observed to be invasive, while after some time it does: plants may propagate exponentially if given the space, so in the beginning they may be rarely observed and after some time seem to be all over the place; it may also be that a certain vector was absent before, like in the case of plants that grow along railways and highways;

climate change may play a role as well (Crooks 2005).

Figure 1. Population development of an invasive species (Branquart et al. 2010)

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Invasibility is the property of an ecosystem to be liable to invasion. It seems, though there is some scientific debate about this, that a diverse ecosystem is in the best position to withstand invasion. Although it may have many ecological niches, which the newcomer may choose from, it are the more uniform pioneer vegetations that are really more open, also in the physical sense, that these are more suitable for invasion. This is corroborated by our observation (see Antigonon below) that some plants invade disturbed areas and not the natural vegetation. This may also in part be caused by the fact that these wastelands are more fertile than the natural parks. They have originally been selected by farmers for that reason too and some plants benefit from higher nutrition levels (and soil structure) more than others.

2.1.2. Phases of invasion: the basis for a classification of invasive species.

In the invasion process of exotic species various stages can be distinguished (Davis 2009). Table 1 shows the categories that are distinguished in this report. These are based on the stage in the process, which is a result of different types of barrier (Branquart 2007). The possible management actions follow from the type of barrier and the stage of invasion.

Table 1. Stages of invasion

Category Stage Barrier Action

Exotic Introduction Geographic Prevention

Established Acclimatisation Environmental Eradication Naturalised Naturalisation Reproductive Containment

Invasive Expansion/spread Dispersive Mitigation

Adapted after Branquart 2007.

Exotic

Species that are not part of the natural indigenous vegetation are called exotics. Examples are introductions as ornamental or agricultural species. If contained within the confines of gardens and farms, these species are not considered problematic. Even if they ‘escape’ into nature, meaning that they live outside the immediate control of man, but do not reproduce effectively, these species are not considered here. Typical example is banana.

However, if species are known to be invasive in other comparable environments, for instance in the case of the Dutch Caribbean if they are known from neighbouring islands, then it is important to keep the species away from the territory. The chances are big that people will help the species transgress the natural geographic barrier, on purpose or by accident. Therefore, strict prevention measures at borders and coasts are needed to prevent this to happen.

Established

Species that occur ‘in the wild’, i.e. outside the control of cultivation or husbandry and are able to reproduce themselves resulting in new individuals, we call established (present). Species can stay in this phase, the ‘lag phase’ (see 2.1), for quite some time. It is the stage in which the species adapts to its new environment using its genetic flexibility.

At this stage complete eradication is still an option, because the number of individuals and locations is limited. This means that the costs can be relatively low, compared to eradication at a later stage. A typical example is Azadirachta, the neem.

Naturalised

If given enough time, species may start to adapt genetically to the new environment, by optimising its physiology and/or growth habit. As a result the species will start spreading more rapidly and effectively and becoming part of the natural flora. In most cases this is not considered a major problem; the plants will get their own function within the ecology of the

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island and will not replace indigenous species entirely. Moreover, the costs of complete eradication have become prohibitive at this stage, so only containment is an option.

This means that one can no longer control the species at all sites, but may still be able to do so in vulnerable habitats. With some effort a sort of status quo can be achieved. A typical example is Cryptostegia on Saba.

Invasive

It is generally believed that about one in one thousand exotics becomes really problematic, e.g.

with respect to environmental, ecological or economical impact (Williamson 1995). They start to grow out of control, massively invade natural habitats and reduce or eliminate native species.

They have broken down the dispersal barrier and have become invasive.

At this stage one can only try to achieve a stage of equilibrium, of mitigation, by intensive control measures. These are usually limited by financial resources, and can normally only be successful with commitment of the local society, e.g. shown by the enthusiastic support and hand labour of many volunteers. A typical example is Antigonon on St. Eustatius.

Interestingly, the statistics of exotics becoming invasives seem to be very different for the Caribbean region. Kairo et al. (2003) report that 446 out of 552 known exotics become naturalised or invasive. This can in part be explained by differences in definition for these categories, but cannot explain the discrepancy entirely. It must therefore be assumed that exotic species in this region have a stronger tendency to behave more aggressively, or in complement, the islands are more vulnerable for invasions; their invasibility is larger. A similar phenomena has been observed by Vitousek et al. (1996) who noted that the percentage of non- native species tends to be greater on island habitats. The size of the island as well as the proximity to other islands or main land seem to play a role. While Cuba and the Solomon Islands have relatively low percentages of non-native species (around 6%), these figures are 65% for the Bermudas, and between 40 and 50% for the majority of the islands in the Pacific and about 20% for the Bahamas (no further data on Caribbean islands).

Table 2. Exotic (alien) species in the Caribbean by type or organism. (Kairo et al.

2003)

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Whether a true effect or not, there seems to be all reason to be vigilant regarding introduction of new species.

2.2. Field visits and information sources

A study visit was made from 2-22 April 2011, during which the three islands of Caribbean Netherlands have each been visited for 5-6 days. The trip ended with a 2 day visit to St. Marten.

The team consisted of Drs. John de Freitas MBA (Carmabi) and Dr Bert Lotz and Ir. W. Joost van der Burg (both Plant Research International). Extensive trips were made to visit all representative vegetation types and sites known to have problems with invasive plants.

2.3. Stakeholders consultation

Discussions were held with the most relevant stakeholders present at the time. For a list of consulted persons, see Appendix I. Focus of the discussions were the problems with invasives as perceived by local organisations, officials and individuals. Local experts were consulted wherever possible.

2.4. Literature search

A preparatory desk study of available literature was performed during early 2011. The provisional list of invasive species as was available at the time was used as a guideline for more specific literature searches. An important source of background information was also provided by the book of Mark Davis (2009) which gives an overview of the current status of the research on invasive species. Where relevant for this report, literature is being cited and references are provided in Chapter 8. Literature.

2.5. How we report the results

After a general chapter on the islands with their specific geographic and social properties which is given in chapter 3, the findings of the study visits related to plants are presented in chapter 4.

The species are presented alphabetically with a short resume of the state of knowledge (4.1.1.).

After that, the most important invasive species are discussed (4.1.2.). These are the species having a strong impact on more than one island. In 4.1.3 a list is provided with plant species of which the status is not clear yet. Finally a list is provided in Appendix II summarising the status of the species mentioned in 4.1.1.

This classification is in line with that which is frequently being used for invasives (see also chapter 2.1):

1. Species that are known to have a negative impact and are already widespread. For these species eradication is no option and a form of management shall be applied to control the situation; to prevent it from becoming worse.

2. Species with the same negative impact on environment, nature, economy, or plant, animal or human health, but that are present in restricted locations. Species belonging to this group may possibly be eradicated, though usually at considerable effort and costs.

3. Species that have not yet arrived on a particular island, but are a potential danger and shall be controlled at ports and airports and eradicated as soon as they are spotted in cultivation or the wild. These are usually put on a ‘Black List’.

Chapter 4 ends with an enumeration of recommendations and/or policy priorities per island.

Chapter 5 gives general discussion and conclusions.

Chapter 6 enumerates all recommendations given in the previous chapters.

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Chapter 7 acknowledges the main informants.

Chapter 8 contains the most relevant literature.

Finally, the appendices present the itinerary and the people consulted and a checklist with an indication per island of the status of invasiveness.

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3. The islands: general

3.1. Bonaire

LAND AREA 288 km2 HIGHEST MOUNTAIN Brandaris, 240 m HUMAN POPULATION 14,000 CAPITAL Kralendijk

Bonaire is located in the Southern Caribbean Sea (between 68º11’ and 68º25‘ W and12º2‘ and 12º19‘ N) about 87 km north of the coast of Venezuela and 40 km east of Curaçao.

CLIMATE

Bonaire is an island that forms part of the so-called ‘Caribbean dry region’ (Sarmiento1976) situated between the Araya Peninsula in Venezuela (64° W long., 11° N lat.) and Cartagena in Colombia (75° W long., 10.5 N lat.). This region is characterized by the presence of semi-arid areas with rainfall below 800mm/yr and arid areas with rainfall below 500mm/yr. With its 30 yr.

average of 463 mm/yr (1971-2000; Meteorological Service of the Netherlands Antilles, pers.

comm.) Bonaire belongs to the latter category. Rainfall on the island is seasonal, with the last three months of the year accounting for 51% of the long-term annual average. Only in November is the average monthly rainfall almost 100mm, the critical point below which evaporation exceeds precipitation in tropical areas (Beard 1949; Nix 1983).

TOPOGRAPHY

Bonaire is 35 km long, 8–15 km wide, and consists of a volcanic core, surrounded by limestone formations. The northern end of the island, within Washington-Slagbaai National Park, is dominated by hills including Mount Brandaris, the island’s highest point. The flat, low elevation southern end of

the island

contains the Pekelmeer , once a series of natural shallow lagoons that have been modified over hundreds of years

for salt

production.

Bonaire has jurisdiction over an offshore island—Klein Bonaire —situated c.1 km from the central west coast. Klein Bonaire is a low coral-limestone island fringed with sandy beaches.

GEOLOGY

Broadly speaking, on Bonaire the rocks at the surface can be divided in two different groups, namely the volcanic Washikemba Formation and limestone formations (De Buisonjé 1974). The

Figure 2. Washington Slagbaai National Park

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Washikemba Formation is named after the Washikemba plantation in eastern Bonaire. It is a heterogeneous, submarine volcanic succession of mid-Cretaceous age (~90 – 100million years ago) and largely consists of basaltic, andesitic and daciticlavas, sills and dikes, interbedded with, or intrusive into volcanic (tuffs) and biogenic (cherty limestones) sediments. The thickness of this succession is approximately 5 km. The Cretaceous rocks of the Washikemba Formation are exposed in the northwest of Bonaire from Slagbaai to Rincón, and in the east of Bonaire from Bolivia to Seru Largu.

In both regions the rocks dip 45 to 60 degrees to the northeast (Pijpers 1933). These two areas are separated and rimmed seaward by limestones of Eocene, Neogene and Quaternary age, which unconformably overlie the Cretaceous sequence. The dacitic lavas are the most resistant to weathering. They form the highest terrains of the island (e.g. Brandaris, Yuana, Seru Mangel, Seru Wekua). As they alternate with more easily weathered volcanic sediments, the terrain is rocky and can be strongly uneven. The basalts and basaltic andesites, on the other hand, are often deeply eroded and their outcrop areas give a more undulating terrain. A good example of this is the area in the west between Saliña Slagbaai and Goto Meer, and also a large part of the outcrop area of the Washikemba Formation in the south. The sharp hills in the latter area consist again of dacitic lavas and dikes. The limestone formations are a predominantly Neogene sequence of calcareous forereef deposits (the Seroe Domi Formation) partially overlain by Quaternary reefal limestones.

VEGETATION

The island’s vegetation is generally xerophytic with many areas dominated by columnar cactus intermixed with low scrub and large expanses of land largely devoid of vegetation, especially along the eastern shoreline which receives slightly less rainfall on average than the western side of the island. Virtually all trees on the island were removed by the early nineteenth century and woody vegetation continued to be cut for charcoal production into the twentieth century.

Grazing animals were introduced by 1700 and have significantly altered the vegetation. Free roaming goats and donkeys have continued to have an impact in many areas even to the present day. In some regions, notably within Washington-Slagbaai National Park, there are patches of thicker and taller (3–4 m) thorn scrub forest supporting some epiphytic growth. Lac Bay on the south-eastern side of the island supports Bonaire’s only significant mangrove woodland (Wells & Debrot 2011)

3.2. Saba

LAND AREA 13 km2; HIGHEST MOUNTAIN The Mountain, Mount Scenery, 877 m.

HUMAN POPULATION 2,000; CAPITAL The Bottom

Saba is located at 17º38' N latitude and 63º14' W longitude (De Palm 1985). The island, like St.

Maarten and St. Eustatius, is part of the island arc of the Lesser Antilles, extending from the Virgin Islands to Venezuela. The distance from Saba to St. Maarten is 48.1 km. (in a straight line), Saba and St. Eustatius are 33.6 km from each other (Land Register, 1997).

CLIMATE

The climate of Saba is tropical (the average temperature in the coldest month lies above 18º C) and according to the system of Köppen (1931) falls between a savannah- and monsoon-climate (Stoffers 1956). The average rainfall is 1101.3 mm per year (1891-1980, rain station in The Bottom), but the variation in yearly rainfall is large (De Palm 1985). The monthly rainfall is very irregular too. No clear wet or dry season can be distinguished. Every 'wet' month may be dry and every 'dry' month may be wet. The average values over a large number of years do indicate however, that the least rain falls in February, March and April while the most rain falls in August, September, October and November. In those wet months the average rainfall is almost two and a half times as much as in the dry months. Lazell (1972) calls Saba and St. Eustatius “Snag-

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islands”. This type of island has one high peak (more than 600 m high) that arrests a few clouds and is able to hold on to them mainly because of evaporation from the island itself. The lowland of Saba is very dry. According to Veenenbos (1955) The Mountain on Saba has an estimated annual rainfall of 1500-2000 mm. The type of vegetation does in fact indicate this, exact data are lacking however. Augustinus' report (1985) indicates that differences in rainfall on Saba appear to occur above the critical height of 450 m. Rainfall there increases with height till it reaches a maximum on the top of The Mountain. The average yearly temperature on Saba is probably the same as on St. Eustatius: 25.7º C (De Palm 1985). The temperature drops however, with increasing height. In August 1980 the average day temperature at 600 m was 23º and at 800 meters 22º (Augustinus et al. 1985).

The top of The Mountain is almost constantly veiled in clouds (Van ‘t Hof 2010). The relative humidity in August 1980 varied between 90-98% at a height of 600 meters and between 90- 100% at 800 meters (Augustinus et al. 1985).The dominant wind direction is east. Saba is situated in the Atlantic hurricane zone. On average one tropical storm or hurricane passes at a distance of less than 200 km each year. Once every 4 or 5 years hurricane conditions occur (De Palm, 1985).

TOPOGRAPHY

The island of Saba has an area of roughly 13 km² (De Palm, 1985). The island actually consists of the upper part of a volcano steeply rising from the sea. The lowest part is situated beneath the sea, which is more than 600 meters deep around the island. The highest point of the island is the top of the volcano, called The Mountain or Mount Scenery, which is 877 meters high.

Around the top there are several lower elevations, like Troy (586 m.), Mary's Point Mountain (566 m), Peter Simmons Hill (223 m), Great Hill (423 m), Peak Hill (401 m) and Old Booby Hill (223 m). Weathering and erosion formed numerous deep, radially running ravines (so-called 'guts'). There are only a few flat areas. The largest is the valley where the little town The Bottom is situated. Another flat area is called Flat Point. Here the runway of the airport was built. The sea has steadily undermined the sides of the island, causing them to be very steep or even vertical. There are no permanent sand-beaches on Saba, only small rubble-beaches.

Figure 3. Saba from a distance

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GEOLOGY

It may be assumed that the first eruptions with which the Saba volcano's sub-marine phase started, date from the Middle or Upper-Pleistocene era (± 500.000-10.000 years ago), while the latest volcanic processes possibly continued till the middle of the Holocene (± 5.000 years ago) (Westermann & Kiel 1961). The volcano has been dormant for a considerable time. Roobol &

Smith (2004) estimate the time of the last eruption between 1610 and 1675. The typical cone shape of so many volcanoes has not been preserved above sea level, below sea level however, this form still exists (Westermann 1957). The lower parts of Saba consist mainly of agglomerates and tuffs (Westermann & Kiel 1961). In essence it is a strata-volcano, in which pyroclastic material dominates andesitic lava-streams. In the higher parts andesitic lava-layers become more numerous. Two lava-streams that erupted during the younger phase of the volcano now form the striking formations in the northwest of the island: Behind the Ridge and Flat Point. There are no craters on Saba. A viscous lava plug formed in the original main crater of the stratovolcano in the last active period, closing the entrance. Mount Scenery is the top of the volcano with the cooled lava plug. Before complete dormancy the volcano had a stage in which there were no real eruptions anymore but there was some activity such as the outpouring of sulphurous gases, coming from not quite hardened magma in the deep (Westermann 1957).

This caused the sulphur and gypsum layer of Behind the Ridge, part of which was exploited in the 19th century. The old mine tunnels still exist. The only recent and notable manifestations of post-volcanic activity are the hot springs on the beach between Ladder Point and Tent Point (Westermann & Kiel 1961) and near Green Island along the north coast (Van ‘t Hof, pers.com.).

3.3. St. Eustatius

LAND AREA 21 km2; HIGHEST MOUNTAIN The Quill, 602 m.

HUMAN POPULATION 2500; CAPITAL Oranjestad

St. Eustatius (‘Statia’) is located at 17.30º N and 73º W (De Palm 1985). The island, like Saba and St. Marten is part of the island arc of the Lesser Antilles, extending from the Virgin Islands to Venezuela.

CLIMATE

The climate of St. Eustatius is tropical (the average temperature in the coldest month lies above 18 ºC) and according to the system of Köppen falls between a savanna- and monsoon-climate (Stoffers 1956). The average rainfall is 1072.7 mm per year (1881-1980, Oranjestad) (De Palm 1985), but the deviation of yearly rainfall is large. The monthly rainfall is very irregular too. No clear wet or dry season can be distinguished. The average values over a large number of years do indicate however, that in February, March and April the least rain falls while in the most rain falls in August, September, October and November. In those wet months the average rainfall is twice as much as in the dry months. Lazell (1972) calls St. Eustatius and Saba “Snag-islands”.

This type of island has one high peak (more than 600 m high) that arrests a few clouds and is able to hold on to them mainly because of evaporation from the island itself. The lowland of St Eustatius is very dry. Indeed the low-lying rain-stations (at 25 and 40 m) collect on average a little less rain than a higher-lying station (at 300 m). According to Veenenbos (1955) The Quill (above 400 m) has an average rainfall of 1500-2000 mm, however, there are no rain-stations above 400 m, so numbers cannot confirm this. The average yearly temperature is 25.7º C (1959-1980; De Palm, 1985). The change in temperature all through the year is small. January is on an average the coldest month with 25.2º C and August is on an average the hottest month with 28.0º C. The temperature drops however, with increasing height. It is to be expected that on average on top of The Quill the temperature is a little lower. The dominant wind direction is east. St Eustatius is situated in the Atlantic hurricane zone. On average one tropical storm or hurricane passes at a distance of less than 200 km each year. Once every 4 or 5 years hurricane conditions occur (De Palm, 1985).

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TOPOGRAPHY

The island of St. Eustatius has an area of roughly 21 km² (Westermann & Kiel 1961). It is more or less egg-shaped with the broadest part in the southeast. The northwest and the southeastern part are hilly and the area in between is almost flat. The hills in the northwestern part are called The Mountains or The Little Mountains. They are rather low, but they have steep slopes. The highest top is “Boven”

(294 m). “Bergje”, also called Little Mountain, is 223 m high and Signal Hill reaches up to 134 m.

There are two well developed valley systems in The Mountains (Westermann & Kiel 1961), that run into Venus Bay at the east side and Tumble Down Dick Bay at the west side. Along the west

coast of The

Mountains there is a very steep cliff. The southeastern part of the island only consists of one hill, a sleeping volcano with a wide and deep crater, The Quill. This name is a corruption of the old Dutch name “De Kuil”. Westermann & Kiel (1961) call this volcano perhaps the most beautiful example of this type in the Antilles. The edge of the crater is highest at the eastern side (601 m) and lowest at the Westside (378 m).

The bottom of the crater lies at 273 m. above sea level. The craters shape is almost round. The slopes on the inside are extremely steep. The outer slopes are more gradual, however several steep ravines cut into them. The northwestern slope of The Quill changes into an almost flat area that extends to The Mountains. This low-lying, slightly sloping plain between both hill areas is called “De Kultuurvlakte”. All along the southeastern and center part of the island the coast consists of a sheer cliff, on average about 30 meters high (Westermann 1957), except at Billy Gut and Concordia Bay where you can find sand beaches. At the base of the cliff on the west side of The Kultuurvlakte below Oranjestad there is also a sandy beach.

GEOLOGY The whole southeastern part of the island is taken up by one big volcano, The Quill that is unique because of its even form. The Quill is also a beautiful example of an ash-volcano (Westermann 1957). This one originates from the Holocene (Holocene: 10.000 years – present day). The unique form took shape in the last phase, when there was no lava-flow anymore, but magma was exploding and blown away as a spray by gas pressure. Especially the last eruptions must have been violent, since only loose material was thrown out. The entire top, crater, slopes and the base of the volcano are covered with loose material. The largest blocks are lying on the edge and on the bottom of the crater. Lower on the slopes the material gets finer and The Kultuurvlakte is covered for the greater part by volcanic ashes. The finer material was blown in western direction by the trade wind. Thus the base of the volcano lies on the remains of the old volcano. The various strata of ejected material can still clearly be seen in the coastal cliff. The Round Hill probably is a small adventitious crater, which afterwards was covered with ashes. In historical times there were no further eruptions. The cone of the volcano however, shows little erosion, which indicates a relatively recent sleeping phase (Westermann 1957).On the south side of The Quill we find a totally different rock of sedimentary origin. These are two slabs

Figure 4. Heavy clouds over St. Eustatius

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reclining against the slope of the volcano: The White Wall (270 m) and The Sugar Loaf (73 m).

They consist of limestone originating from corals and shells, alternated with some volcanic material. Their age is determined to be roughly 70.000 to 21.000 years old (Westermann & Kiel 1961). The limestone was originally formed at the bottom of a shallow sea near the then still small Quill-volcano. The horizontally constructed slabs were forced upwards during the active phase of the volcano and were turned over by a plug of lava (now hardened) (Westermann 1969).

3.4. Other Dutch Caribbean

3.4.1. St. Marten

(= St. Maarten + St. Martin)

LAND AREA 86 km2; HIGHEST MOUNTAIN Pic Paradis, 424 m (French part) HUMAN POPULATION 14,000; CAPITAL Philipsburg

St. Maarten is located at 63º N and 18º W (De Palm 1985). The island, like Saba and St.

Eustatius is part of the island arc of the Lesser Antilles, extending from the Virgin Islands to Venezuela (Westermann 1957). St. Marten is the largest of the three Windward Islands of the Netherlands Antilles, and has an area of about 86 km² (De Palm 1985). However, since 1648 it is divided in two parts: the present Netherlands Antilles part and the French part. The northern and largest part is French (with an area of ±52 km²) and the southern and smallest part belongs to the Netherlands Antilles (area of ±34 km²). Several uninhabited small islands fall under the jurisdiction of both parts of St. Marten. Tintamarre, also called Flat Island, Ile Pinel, Little Key and Green Key at the eastern side of the main island and Great Key in Simpson Bay Lagoon belong to French St. Martin. Pelican Key, also called Guana Key, Molly Beday and Hen and Chickens at the eastern side of the main island, and Little Key in Simpson Bay Lagoon belong to the Netherlands Antillean part of St. Maarten.

CLIMATE

The climate of St. Maarten is tropical (the average temperature in the coldest month is above 18º C) and according to the system of Köppen falls between a savannah and a monsoon climate (Stoffers 1956). The average rainfall is 1008 mm per year (1961-1990; CBS, 1996), but the deviation of yearly rainfall is large. In 1994 for instance, there was only 658 mm of rain, whereas in 1992 it was 1273 mm. The monthly rainfall is very irregular too. No clear wet or dry season can be distinguished. Every dry month can be wet, and every wet month can be dry. The average values over a large number of years do indicate however, that February and March are the months with the least rain, while most rain falls in September, October and November. In those wet months the average rainfall is trice as much as in the dry months. There are no hills of sufficient height to stop the clouds; this is why there is no big difference in rainfall between the higher and lower parts of the island. Nevertheless Stoffers (1960) suggests that on top of Sentry Hill there is more rainfall than lower on the slopes and according to the ECNAMP report (1980) too, there is supposed to be considerable more rainfall in the hills in the middle part of the island than in the lower parts. The official figures give no definite answer. The figures published by CBS are collected at a rain-station at Princess Juliana Airport. The average yearly temperature is 26.8 ºC (1961-1990; CBS, 1996). The temperature variation over the year is small. January and February are on an average the coldest months with 25.2º C, and August and September are on an average the hottest months with 28.2º C. (1961-1990; CBS, 1996).

The dominant wind direction is east (De Palm 1985). St Marten is located in the Atlantic hurricane zone. On average one tropical storm or hurricane passes at a distance of less than 200 km each year. In September 1995 the centre of a severe hurricane, called Luis, passed over St.

Maarten. This hurricane caused severe damage.

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TOPOGRAPHY

St. Marten has an irregular shape because of the many large and small bays and lagoons along its coast. The lagoons are closed off from the sea by sandy embankments. Simpson Bay Lagoon is the largest lagoon. The island has a great many beaches. Most of the sandy beaches are on the south- and northwest coast. The Landscape is hilly except in the Low Lands on the west side. Three hilly ridges run over the island in a northwest direction. The highest top is the top of Mount Paradise at 400 meters on the French side. Flagstaff is the highest hill on the Netherlands Antillean side, reaching 386 meters.

GEOLOGY

The oldest rock strata of St. Marten are about 50 million years old (Westermann 1957). These strata were deposited in the ocean. They consist of rubble from erosion of the small volcanic islands in the area on the one hand, and of marine deposits on the other hand. These strata were folded and lifted upwards by tectonic forces in later periods. They were temporarily above sea level. These oldest rocks, the Pointe Blanche Formation consist of very hard, partly pebbly tuffs. These were most resistant against eroding forces and now remain as two parallel ranges rising from the island. The highest tops belong to this formation: Fort Hill (220 meters), Cole Bay Hill (215 meters), Sentry Hill (344 meters), Saint Peters Hill (317 meters), Flagstaff (386 m), Mount Paradise (400 m), and Naked Boy Hill (300 m). This period of uplifting was accompanied by rising magma. During the course of a period of local subsidence of the earth's crust in the Miocene (30 to 16 million years ago), the Pointe Blanche strata were submerged below sealevel. During the coldest period of the ice age in the Pliocene (1 mln to 10.000 years ago) sea level was at least 36 meters lower than at the present time. Anguilla, St. Barths and St. Marten were then part of one big island. On this island a giant rodent (Amblyrhiza inundata (De Palm, 1985) lived. Remains of this animal are found in St. Marten as well as Anguilla. At the end of the Pliocene (± 10.000 years ago) the ice masses melted and seal evel rose. The island was flooded and only the highest parts, the present islands Anguilla, St. Barths and St. Marten remained above sea level. These islands are now situated on a submarine plateau, with a maximum depth of 36 meters and called the Anguilla Bank. Great Salt Pond and Great Bay are actually a drowned valley in which at the spot where Philipsburg is situated now, a layer of marine shell sand was deposited. The other bays and lagoons are also drowned valleys. The youngest rocks were formed in the sea. They are coral reefs, which due to a small rise of the island are now situated 5 to 6 meters above sea level. They only take up a small area mainly at the east coast of the island

3.4.2. Aruba

LAND AREA 193 km2; HIGHEST MOUNTAIN Jamanota 188 m HUMAN POPULATION 105,000; CAPITAL Oranjestad

Aruba belongs to the Leeward Antilles and has an arid climate. The landscape is characterised by cactuses. Aruba’s tropical marine climate shows little seasonal variation, with an average annual temperature of 27 °C, varying from about 26 °C in January to 29 °C in July (Wikipedia 2011).

Rainfall averages 510 mm or less annually, and the island’s residents rely on one of the world’s largest desalination plants for most of their drinking water. The rainy season occurs between October and December. Permanent rivers are absent. The main mountains are Jamanota, Canashito and Hooiberg, the remainder of the island is flat. The central part of the island mainly consists of rocks of volcanic origin (diabase, tuffs, conglomerates, schists), surrounded by limestone formations. Wild goats and donkeys roam free on the mountain.

The island has hardly any natural resources, arable land covers a little over 10% of the area.

The economy relies almost exclusively on tourism.

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3.4.3. Curacao

LAND AREA 444 km2; HIGHEST MOUNTAIN Christoffelberg 372 m HUMAN POPULATION 142,000; CAPITAL Willemstad

Curaçao belongs to the Leeward Antilles and has a semiarid climate with a dry season from January to September and a wet season from October to December. The temperatures are relatively constant with small differences throughout the year. The trade winds bring cooling during the day and the same trade winds bring warming during the night. The coldest month is January with an average temperature of 26.5 °C and the warmest month is September with an average temperature of 28.9 °C. The year's average maximum temperature is 31.2 °C. The year's average minimum temperature is 25.3 °C. Curaçao lies outside the hurricane belt, but is still occasionally affected by hurricanes, as for example Omar in 2008. Precipitation averages 550 mm per year, with a high in the months of October (84 mm) to December (100 mm). The driest month is March (Wikipedia 2011). The highest point is the Christoffelberg which is 372 m high and lies in the reserved wildlife Christoffelpark. The eastern part of the island is flatter and lower, broken by the flat-topped Tafelberg at Santa Barbara. Just west of town, lie three sharp hills known as ‘Drie Gebroeders’ (three brothers).

Most of the western and southeastern countryside is made up of gently rolling volcanic hills.

Eroded rock washed down from the hills forms a rich soil. The island's plantations grew up in the surrounding valleys. Flora and fauna in these areas is particularly rich. Other rocks are of sedimentary origin, while the entire north coast is made up of four limestone terraces.

The main vegetation is xeric scrubland, with various forms of cacti, thorny shrubs, evergreens, and the island's national tree, divi-divi.

The island has little resources and a large proportion of the economy relies on tourism. 375 km off the coast of Curaçao, to the south-east, lies the small, uninhabited island of ‘Klein Curaçao’

(little Curaçao). It has been denuded by guano mining and flora is being re-established.

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4. Naturalised and invasive exotic plants

4.1. Results

4.1.1. Alphabetical list of invasive plant species

This chapter describes the records from literature, complemented with our findings. We concentrate on the species that are actually present. This includes plant species present in large amounts, causing ecological damage; plants present in smaller amounts and not yet having shown a negative impact on biodiversity (established); and finally plants that are there in small amounts only and of which a tendency to invasiveness is known.

A table with the status (exotic, established, naturalised, invasive) per island is given in Appendix II. Since most species in this list show invasive properties here or elsewhere, only those plants that show invasiveness on the particular island are indicated as such.

Summaries are given in tables 3 and 4.

Table 3. Number of invasive plants per invasive phase and per island

It must be emphasised that the ranking established/naturalised/invasive is in part subjective.

When plants are established, i.e. they are able to maintain one or more stable populations through reproduction, and not massively reproducing nor causing any negative impact on economy or nature (i.e. being invasive), then it is a matter of scale and time before they can be regarded as naturalised.

Table 3 and 4 are referring to the 65 species mentioned in 4.1.1. (as well as in Appendix II).

These are preliminary results as comprehensive and accurate inventories are lacking. Due to the limited time available for prospecting, not all species could be given the attention necessary, and only Bonaire, Saba and St Eustatius could be visited. Therefore a series of known or suspect invasive plant species (over 80 in number) are enumerated in 4.1.3.

More thorough plant inventories shall be made to obtain a more complete picture.

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Table 4. Invasive plants arranged per plant type and per island

Type Aruba Bonaire Curacao Saba St Eust. St Mart.

Fern 2 1

Grass 9 11 12 7 7 9

Herb 4 4 4 5 6 6

Shrub 5 7 7 6 4 6

Succulents 4 4 6 5 4 4

Tree 15 16 18 8 11 8

Vine 4 5 6 8 7 5

Total 41 47 53 41 40 38

Most invasive plant types are represented on all islands. With few exceptions there do not seem many plant groups with a strong preference for a particular type of island. A clear exception is the group of ferns that can only grow well with sufficient moisture, which can only be found on the mountains of the Windward Islands. Bonaire and Curacao seem to be particularly liable to have invasive shrubs and trees. These islands also have a larger proportion of grasses. Saba and St Eustatius have relatively many vines. Curaçao has the highest total number (53) of invasives; which in part may a reflection of the more intensive naturalists’ activity and being the home base of Carmabi.

Nomenclature is following the GRIN database, from the Germplasm Resources Information Network at http://www.ars-grin.gov/.

Presence on the islands is indicated by the following abbreviations: Aruba (A), Bonaire (B), Curacao (C), or ABC; and Saba (SA), St. Eustatius (SE), St. Maarten (SM), or SSS.

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Agave sisalana Perrine (C, SE) – Sisal, pita vlas

Native to Mexico (Howard 1979 vol 3). Imported to Curaçao for fiber production but the experiment failed (Arnoldo 1971). Mentioned as cultivated on Curaçao, St. Maarten and St.

Eustatius (Boldingh 1913). Naturalized on Curaçao (Arnoldo 1971). Found also on St. Maarten (Howard 1979 vol 3). Reproduction is primarily vegetative by bulbils and a plant can bear up to 2000 bulbs (Langeland et al. 2008). It is fast growing, drought tolerant and adaptable to a variety of soil conditions and climates. It grows well in sandy soils and in full sun to partial shade (Langeland et al. 2008).

Albizia lebbeck (L.) Benth. (ABC, SSS) – Barba di jonkuman, lebbeck

This tree is native to tropical Asia and was introduced into the Caribbean as early as 1782 (Dunphy & Hamrick 2005). It is a prominent species in both natural and disturbed habitats throughout the region (Kairo et al. 2003). It was introduced to all six Dutch Caribbean islands as well, and has become naturalized on Curaçao and the Windward Islands (Stoffers 1973, Arnoldo 1971, De Freitas, unpubl. data). Typical traits which give Albizia an invasive edge, include perfect flowers, generalist pollinators, retention of fruit on the tree, nitrogen fixation, use of pioneer habitat, high seed production, high growth rates, and multiseeded fruits (Dunphy &

Hamrick 2005). It is present on St. Eustatius in the English Quarter (Boldingh in Stoffers 1973), on Saba in The Bottom (Stoffers 1973).

Aloe vera (L.) Burm.f., syn. A. barbadensis Mill. (ABC, SSS) – Sentebibu, aloe, Barbados aloes, common aloes

The plant is native of the Mediterranean (Arnoldo 1971). Established/naturalized on all six Dutch Caribbean islands (Arnoldo 1971). Boldingh (1909; 1913) reports it for the ABC islands and only for St. Eustatius and St. Maarten. It is also present on Saba near the harbour.

Figure 5. Aloe vera on Bonaire

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Antigonon leptopus Hook. et Arn. (ABC, SSS) – Coral vine, corallita, bellísima

(for a more detailed treatment see 4.1.2)

Elsewhere in the Caribbean, this species is invasive in Antigua, Bahamas, the Dominican Republic and Haiti (Kairo et al. 2003). In Curacao, Bonaire and Aruba, this species only thrives in areas with heavy disturbance by man, and generally penetrates undisturbed vegetation only in very limited numbers. In Curacao the species has been found in a few relatively undistur- bed areas such as Roi Rincón and the Higher Terrace of Noordkant, probably associated with the illegal dumping of garden clippings. It is surprising that it has not become more widely spread as its seeds have become an important food of the native pigeons.

On St. Eustatius A. leptopus has been found in three vegetation types and is dominant in one of these (De Freitas et al. The landscape ecological vegetation map of St. Eustatius, in prep.). In 2007 the vine covered 15-20 percent of the total land area of St Eustatius (Figure 38). On Saba it invades roadside areas, habitats heavily disturbed by goats and areas affected by erosion such as along the road through Fort Gut (Debrot pers. obs.).

Arivela viscosa (L.) Raf., syn. Cleome viscosa L., Polanisia viscosa (L.) DC.

(ABC, SSS) - Wild massamby, kaya- kaya

This weedy herb is native of the Old World tropics (Stoffers 1982). Naturalized on all six Dutch Caribbean islands (Boldingh 1909, Stoffers 1982, Van Proosdij 2001). It occurs mostly in open places and disturbed locations. It is a weed of roadsides, waste grounds, cultivated fields, sandy and rocky seashores. It is widely naturalized from central United States southward through Central America, the West Indies, and northern South America (Howard 1979). On St Eustatius it forms a pest in horticultural fields (pers.obs. Van der Burg). It was already established on the Windward Islands at the beginning of the 20th century (Boldingh 1909, 1913).

Figure 7. Antigonon leptopus, an attractive climber (St Eustatius)

Figure 6. Arivela viscosa op St Eustatius

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Asystasia gangetica (L.) T.Anderson, syn. Asystasia coromandeliana Nees, Justicia gangetica L., Ruellia zeylanica J.Koenig ex Roxb. (ABC, SSS) - Chinese violet

Native of tropical Africa and India (Langeland et al. 2008), now a pantropical weed (Arnoldo 1971; Howard 1989 vol 6). In the Caribbean region naturalized in Central America, Puerto Rico, and the Virgin Islands (Langeland et al. 2008). Naturalized throughout the Pacific. Cultivated on ABC & St. Maarten (Arnoldo 1971). Is naturalized on beaches in St. Maarten (Arnoldo 1971), along roadsides in Saba (pers.obs. Van der Burg) and in hedges bordering vegetable gardens in St. Eustatius (pers.obs. Van der Burg). Introduced in Florida in 1930 possibly as an ornamental/ground cover, and found naturalized by 1970. (Langeland et al. 2008). It is a very vigorous ground cover and can be very invasive in developed or natural landscapes. If supported by hedges it can grow up to 2 m high in Suriname (Van der Burg, pers.obs.). A very successful colonizer that has invaded across a wide geographical range due to its fast establishment, rapid growth rate and early flowering. Naturalized in many of the Hawaiian islands in disturbed forest communities (Langeland et al. 2008). Its entry is prohibited in Australia where it is considered a weed that poses a significant threat to biodiversity (Langeland et al. 2008). This species can be highly invasive. It can smother any vegetation with its herbaceous layer. On the Pacific Islands it has caused major disruptions in native ecosystems (GSID 2011). It is adapted to a wide range of environmental conditions and will tolerate drought, full sun to partial shade, direct exposure to salt spray and a variety of soils (Langeland et al. 2008). It is extremely competitive and can absorb significant amounts of soil nutrients and form extensive, viable seed banks. Reproduces by vegetative fragments and seed, and flowers and sets fruit early in its life cycle (at only 45 days old) and can produce hundreds of explosive capsules per plant. As seeds mature, germination percentages increase and temperature requirements become less sensitive (Langeland et al. 2008).

Figure 8. Asystasia gangetica on Saba

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Azadirachta indica A.Juss (ABC, SE, SM) - Neem

(for a more detailed treatment see 4.1.3)

This species has been widely introduced in tropical regions for wood production (e.g. Campbell 2005) and as an ornamental of medicinal value and is listed as an invasive in Puerto Rico, Antigua, Barbuda and the Dominican Republic (Kairo et al. 2003), as well as other areas where it is not native (e.g. Campbell 2004). For Australia, where it is also spreading rapidly, the assessment of its potential impact remains inconclusive (Csurshes 2008). Once introduced it is typically not used for its intended purpose (Judd 2004). Due to its invasive properties, the Peace Corps which formerly promoted the species, now discourages its propagation (Judd 2004).The species is very drought resistant, and in both Curacao and Bonaire and St. Maarten the species is therefore able to invade dense vegetation, requiring little disturbance for it to spread. Its seeds are dispersed by rats (Rattus rattus) and native birds (e.g. Mimus gilvus) (AOD, pers.

obs.). In the 1980s reported for only Anguilla, Antigua, St. Kitts, Montserrat and Guadeloupe (Howard vol 1).

Balanites aegyptica (L.) Delile (B, C) - Lamunchi shimaron, korona di Hesus

This species is native to the arid areas of West and Central Africa. It has been introduced into cultivation in Latin America and India. The wood is very valuable for charcoal production and the leaves are fruits are important food source for goats, camels and other wildlife. The fruit is edible and can be made into a beverage. The seed kernel can be made into bread and soup and contains an edible oil. Several parts of the plant can also be used in combatting pests (Firewood crops 1983). It has a wide ecological distribution, but is mainly found on level alluvial sites with deep sandy loam and free access to water (Schmidt and Jøker 2000). It was introduced in Curacao in 1885 (Arnoldo 1971) and, while formerly distributed from the eastern to mid-central parts of the island, it is now also found on the western side at Knip (De Freitas, Dolfi pers. obs.)

Figure 9. Neem tree on the flanks of The Quill (St. Eustatius)

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Bambusa vulgaris Schrad. ex J.C.Wendl. (SA) - Bamboo

Native to tropical Asia, but widely introduced into tropical and subtropical regions of the world (Howard 1979). Several Asiatic species have been imported to the region for commercial purposes and have become naturalized themselves (Kairo et al. 2006). Bambusa vulgaris is the most widely cultivated exotic species in the region and is naturalized on Saba (NYBG 2011).

Howard (1979) mentions it only for Guadeloupe, Martinique, and Grenada.

Bothriochloa ischaemum (L.) Keng, syn. Dichantium ischaemum (L.) Roberty (B, C) – Yellow bluestem

An Asiatic species now widely introduced in the warmer parts of the world. Originally introduced in the Americas as a pasture grass and is now widespread as a casual roadside, ditch bank, fields and wasteland grass (Stoffers 1963, Howard 1979). Stoffers (1963) mentions it only for Bonaire and Curaçao.

Botriochloa pertusa (L.) A.Camus (SSS) – Pitted bluestem, hurricane grass,

’Donna grass’

(For a more detailed treatment see 4.1.5)

A native of the warmer regions of Africa, India and China; introduced in the Americas (Howard 1979). Open grassy areas, often in disturbed areas Howard (1979) mentions it for Anguilla, Antigua, Nevis, Dominica, St. Lucia, Grenada and Barbados. It is less palatable than the native grasses which it outcompetes, especially on St. Eustatius (Figure 50).

Caesalpinia bonduc (L.) Roxb. (SSS) – Grey nicker

Probably native of eastern Asia (Stoffers 1973).

Shrub common on sandy beaches in the tropics and subtropics. In Saba to be found occasionally at higher elevations.

Invasive on all three Dutch Windward Islands (Boldingh 1909;

Stoffers 1973).

Observed on all three islands and especially

aggressive on St Eustatius and

along the beach on St Martin (Team obs.).

Figure 10. Caesalpinia bonduc on St Eustatius forming impenetrable thorny mats overgrowing the local vegetation

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Calotropis procera (Aiton) W.T.Aiton (ABC, SSS) - Katuna di seda, liberty tree, sprainleaf

Native of the Old World Tropics but widely introduced and naturalized through the New World tropics, including the West Indies. Common and scattered in dry coastal forest, waste places, heavily grazed pastures and beaches up to 200 m (Little et al. 1974). In Boldingh (1909) already

indicated as

naturalized/establishe d on the Windward

Islands. Also

naturalized/establishe d on the ABC islands (Stoffers 1982).

Overgrazing by donkeys leads to a

monoculture of this species on Bonaire. It clearly responds strongly in conjunction with introduced grazers.

Catharanthus roseus (L.) G.Don. (ABC, SSS) – Madalena, churchyard blossom, Madagascar periwinkle

Believed to be native to Madagascar but widely cultivated, escaped and spreading in tropical and subtropical areas (Howard 1989 Part3).

Naturalized on all Dutch Caribbean islands (Stoffers 1982). It is particularly abundant on Saba (Team obs., Figure 12).

Figure 11. Calotropis forest caused by overgrazing at the donkey sanctuary on Bonaire (photo: Debrot)

Figure 12. Catharanthus roseus, naturalised on Saba (near harbour)

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Cenchrus ciliaris L., syn. Pennisetum ciliare (L.) Link (ABC) - Buffel grass

This species, native to Africa, the Middle-East, India, and Indonesia has been widely introduced for livestock grazing (and erosion control and revegetation) in arid and semi-arid areas in e.g.

the U.S.A. and Australia (GISD 2011). One of its competitive advantages on poor and infertile soils is based on its robust root system; its swollen stem base accumulates carbohydrate reserves, so the loss of leaf surface area after drought is not fatal to the plant and allows regrowth in favourable conditions GISD 2011). Buffel grass' dominance and resistance to fire, drought and heavy grazing on arid soils make it a suitable arid zone pasture grass. In Australia, the south-western United States and Mexico (where it has been introduced as a pasture grass and for erosion control) Buffel grass often forms extensive dense monocultures excluding native species and promoting intense and frequent fires. It changes plant communities by encouraging and carrying wildfires through communities that are not adapted to fire. It burns readily and recovers quickly after fire (GISD 2011).

It establishes itself readily in grasslands and expands into other habitats, particularly alluvial flat habitat. It invades hilly areas the slowest. It has a significant negative impact on plant diversity and the fauna as well (Eyre et al. 2009, Smyth et al. 2009) and has been identified as a serious invader in Texas (Flanders et al. 2009), Mexico (Gutierez et al. 2009), Puerto Rico (Kairo et al.

2003) as well as Hawaii as well where it invades and destroys native grassland ecosystems (Daehler & Carino 1998). It forms pure stands in open areas on the ABC islands. It is not tolerant to shade (Tropical forages 2011).

Chenopodium murale L. (ABC, SE, SM)

This herb of up to 1 m high (Holm et al. 1997) is native to Africa (Mediterranean region), temperate Asia (Cyprus, Israel, Jordan, Lebanon, Syria, Turkey), and Europe (GRIN 2011).

Chenopodium murale grows in moist soil (Halvorson & Guertin 2003, Felger 1990, Parker 1972) and disturbed areas (Felger 1990). It is adapted to many ecological conditions but favours soils rich in nitrogen (Holm et al. 1997). It can grow on shaded or open sites (Holm et al. 1997).

Established on St. Maarten and St. Eustatius (Boldingh 1909) and the ABC islands (Boldingh 1913; van Proosdij 2001).

Cleome gynandra L., syn.

Gynandropsis gynandra (L.) Briq. (ABC, SSS) - Yerba di kaya, massamby

Naturalized on all six Dutch Caribbean islands (Stoffers 1982; Boldingh 1909, 1913, 1914). A native of tropical Africa and Asia; introduced into tropical America (Stoffers 1982). It is a weed of waste grounds, fields, roadsides, wet or dry woodlands or wood clearings, and rocky and sandy shores (Howard 1988). It is invasive in the Dominican Republic (Kairo et al. 2003).

Figure 13. Cleome gynandra on St. Eustatius

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